A print head of a dot printer, based on a wire style, is disclosed, for instance, in Japanese Patent Laid-open No. 52-46929 and Japanese Patent Laid-open No. 61-121958, wherein a printing operation is performed by hitting a base section of a print wire with a tip of an armature fluctuated and driven by excitation of a solenoid and making a wire tip thrust from the print head. Another type, based on a stylus style as disclosed, for instance, in Japanese Patent Laid-open No. 62-242549, wherein an armature with a stylus is mounted via a flat spring onto a basic body of the print head in a manner allowing fluctuation and printing operation is performed by fluctuating and driving this armature by excitation of a solenoid and making a stylus of said armature thrust from the print head.
The print head based on a wire style has a defect that when a wire guide hole formed on the print head or the wire is worn a mating state between the wire guide hole and the print wire becomes loose and it becomes harder to maintain the initial precision in dot positioning. In other words, in this style, it is possible to realize an extremely high precision in dot positioning by making higher working precision of the wire guide, but it is difficult to maintain the dot positioning precision for a long time.
In a print head based on a suction stylus style, fluctuation of an armature is restricted by a flat spring connecting a basic body of the print head to the armature, and additionally it is rare for a flat spring which repeats simple flexing movement to wear or get permanently deformed, so that the print head base on this style has more excellent durability than that of a print head based on wire style and the initial dot positioning precision can be maintained for a long time.
In this conventional style, as the flat spring is flexed in the reverse direction when the armature is in a hitting position for printing, because of a force working from a side of the armature, the flat spring may be distorted. In other words, a force on the flat spring, which has been flexed and is forming a secondary curved surface from a direction different from the flexing direction, causes distortion of the flat spring. In brief, in the print head based on the conventional suction stylus style, it is possible to maintain the initial dot positioning precision for a long time, but as the initial dot positioning precision includes a horizontal deflection error of the armature associated with distortion of the flat spring, a precision in repetition of the initial dot positioning itself has a problem.
Also, in a spring charge stylus style, wherein a flat spring is flexed by a permanent magnet to keep an armature in a stand-by position and printing operation is performed by fluctuating and driving this armature by excitation of a solenoid, the flat spring becomes flat in a hitting position for printing, and a horizontal deflection error of the armature associated with distortion of the flat spring is small. However, as it is necessary to form a permanent magnet for maintaining the armature in a stand-by position, production cost of the print head is expensive, which is a defect of this system.
Another problem is that, as it is necessary to maintain a hitting force at each wire and a print edge of the stylus at a constant level in relation to all armatures, it is necessary to maintain a final driving force working to the print wire and the stylus at a constant value by maintaining both of a fluctuation stroke of an armature connected to the print wire for thrusting action or an armature with stylus, or in other words a fluctuation and energization range of an armature energized by excitation of the core and an air gap between a plunger and a core absorption surface, of in other words an energizing force working to the armature by excitation of the core at a constant level respectively.
Factors which decide a fluctuation stroke or an air gap of an armature depend mainly on the precision of the parts themselves, e.g., the support member which supports the armature, the core which fluctuates and drives the armature by sucking a plunger section, and the armature stopper which restricts a stand-by position of the armature. Also important are the working precision of the mounting surface to which the parts are mounted. In the conventional types of print head, the mounting surface on which the parts are mounted is extended to surfaces of various members building a print head. Even with excellent working precision of the parts themselves of the mounting surface, an accumulated error related to forms and dimensions of the members to which the parts are mounted may give rise to a fluctuation or an air gap of the armature, hence it is very difficult to maintain the precision at a satisfactory level.